Electronic medication delivery devices such as infusion pumps are an invaluable tool in modern medical treatment. Many infusion pumps, such as the SYMBIQ™ infusion system sold by Hospira, Inc. of Lake Forest, Ill., can be programmed to deliver medications or other medical fluids to patients. The caregiver is then free to perform other tasks related to patient care, recordkeeping, etc. while the medical fluid is being delivered to the patient by the infusion pump 10 through an administration set 16 or infusion line.
In the case of the SYMBIQ™ infusion system the administration set includes tubing and a cassette with an inlet, and outlet and a pumping chamber covered by a flexible membrane 17 located between the inlet and outlet. A pumping mechanism 11 mounted on a pump chassis 13 repeatedly drives or forces a pumping element (a plunger) 15 that is normally in contact with the flexible membrane 17 forward into the membrane covering the pumping chamber and then retracts the plunger in a reciprocating motion. During retraction of the plunger, a passive inlet valve upstream of the pumping chamber opens, which allows fluid to be drawn into the pumping chamber as the plunger retracts. A passive outlet valve downstream of the pumping chamber closes to keep the fluid in the pumping chamber. As the plunger advances, pushing on the membrane covering the pumping chamber, the inlet valve is closed and fluid pressure builds in the pumping chamber until the plunger reaches its full extension or the fluid pressure reaches a predetermined level or cracking pressure. Then the outlet valve opens to allow the fluid to be displaced through the infusion line to the patient. Thus, medical fluids are displaced through the cassette of the infusion pump in a series of pulsing delivery cycles. The rate of fluid delivery can be controlled by a processor that controls the speed of a motor, such as a stepper motor, that moves the plunger. The processor that controls the pumping mechanism 11 is sometimes referred to as the pump mechanism control or PMC 18.
Administration sets usually have a slide clamp located somewhere on the tubing of the set. The slide clamp can be used as one means to close or open the infusion line, often whether the administration set is installed in the pump or not. In the case of administration sets for cassette type pumps like the SYMBIQ™ infusion system, the cassette also includes a selectively pivotable flow stop 14 that is normally closed but is pivoted opened by a distal pressure sensing pin 26 in the pump when the cassette is properly loaded in the pump. Generally the flow stop 14 is arranged to close automatically when the cassette is removed from the pump. The caregiver can also pivot the flow stop manually and open it to allow flow through the infusion line to prime the line, remove air bubbles and the like. Thus, the clamp and the flow stop normally provide two redundant means for preventing free flow in an administration set or infusion line. However, caregivers may forget to close the line with the clamp or need to unclamp the line at various times during installation and removal of the administration set from the pump. During those times, the flow stop is an important means for preventing unintended free flow of fluid through the administration set. Free flow is undesirable because it can result in spillage or waste of expensive or toxic medications when the administration set is not connected to the patient. Unintended free flow can also result in delivery of medication in a volume, rate or duration in excess of that prescribed when the administration set is connected to the patient.
The SYMBIQ™ pump has a motorized automatic cassette loader 20 with a movable carriage 22 that has an opening 24 formed thereon to receive a cassette of the administration set inserted by the user and moves the inserted cassette inwardly toward a fixed seat on the pump. See U.S. Pat. No. 7,258,534, which is incorporated by reference in its entirety herein, for further understanding of the automatic cassette loader assembly. When the caregiver wants to eject the cassette from the pump, the cassette loader automatically moves the carriage and the cassette away from the fixed seat. In the absence of external forces, the flow stop is designed to automatically pivot to its normally closed position. However, it has been discovered that if the caregiver pulls the administration set out of the cassette loader before the cassette loader reaches its fully opened position, the pivotable flow stop may strike the plunger, distal pressure pin, or other parts of the pump and be unintentionally forced opened so as to cause unintended free flow. More specifically, when a cassette is prematurely removed by the user while the cassette loader is opening, the cassette may bump the plunger, the distal pressure pin, or another structure on the pump. The flow stop may pivot and open if the flow stop surface collides with the distal pressure pin or the plunger with sufficient force.
While various things have been considered to address the above-mentioned problems, there is a need for an electronic medication delivery system and method that is able to simply, quickly and accurately detect an unintended or abnormal free flow condition and promptly alert the caregiver of the condition.
Thus, one objective of the present invention is to provide an electronic medication delivery device, such an infusion pump, equipped with a sensing device and method that will automatically detect an unintended or abnormal free flow condition and alert the caregiver of the condition.
These and other objectives, features, aspects and advantages of the invention will be apparent from the drawings, description and claims that follow.